1. Field of the Invention
The present invention relates to a controller for controlling a controlled object with a control algorithm based on a controlled object model.
2. Description of the Related Art
Conventionally, a controller of the above-mentioned kind has been disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-287804. This controller includes a disturbance observer, a sliding mode controller, and a reference model. In the controller, a disturbance estimate and an estimate of a state amount are calculated by the disturbance observer based on a controlled object model, and a reference value of the state amount is calculated based on the reference model. Then, a control input to a controlled object is calculated by the sliding mode controller based on the disturbance estimate, the state amount estimate, and the state amount reference value, such that the difference between the state amount reference value and the state amount estimate converges to a value of 0.
In general, in the case where a controlled object is controlled with a control algorithm based on a controlled object model, if the dynamic characteristic of the controlled object temporarily changes sharply due to a disturbance, a sudden change in a target value, or the like, an excessively large modeling error can occur. When such a modeling error occurs in the conventional controller, since it uses the disturbance observer, the excessively large modeling error is directly reflected in the disturbance estimate, and as a consequence, the difference between the state amount reference value and the state amount estimate might exhibit an oscillatory swing-back behavior or temporarily become excessively large. In short, there is a fear that the control system might become unstable.